The invention relates to a liquefier for the coolant in a vehicle air-conditioning system, the liquefier including finned heat exchange tubes through which the coolant is conducted in cross-current to the inflowing ambient air. The heat exchange tubes are arranged in several rows of tubes that are disposed behind one another in the direction of flow of the incoming ambient air and whose respective heat exchange tubes are interconnected in a cross-countercurrent arrangement. Preferably, but not exclusively, the fin arrangement is composed of foils made of aluminum, copper or alloys of these materials, each having a thickness of less than 0.15 mm.
Such liquefiers for vehicle air-conditioning systems are customary in the trade. In the past, all heat exchange tubes were provided with a common arrangement of fins which were provided, in certain cases already for the purpose of improving the heat exchange, with projection-like interruptions. Such projection-like interruptions were always oriented in such a manner that an optimal heat flow occurred from the tube into the projection of the respective interruption. Accordingly, such projection-like interruptions extended along the connecting line of tubes of the same row of tubes or along the connecting line of immediately adjacent tubes of adjacent rows of tubes. However, the heat flow between adjacent tubes of the same row of tubes or immediately adjacent rows of tubes is not reduced thereby. Moreover, the pattern of such projection-like interruptions which increase the efficiency of the heat transfer is uniformly distributed over the entire fin arrangement.
In these prior art liquefiers, the good heat-conductive connection between adjacent rows of tubes in the fin arrangement through which the medium flows in opposite directions causes an average temperature level to be established which has a performance reducing effect. This reduction in performance is so distinct that a cross-countercurrent, which theoretically is able to produce a considerably higher effective temperature difference, brings practically no improvement in performance compared to a simple cross-current. This effect is augmented in liquefiers for the coolant of a vehicle air-conditioning system in that the tubes of adjacent rows of tubes (considering in each case in the direction of flow of the ambient air) are very small and thus the flow of heat transferred by way of the fin arrangement between the tubes of adjacent rows of tubes is particularly great. In the present connection, the particularly serious heat losses due to heat conduction are given exclusive consideration while the heat losses due to radiation, which are smaller by about one order of magnitude, are not to be considered here.
A prior art liquefier, German Gebrauchsmuster (utility model) 1,685,651, for the refrigerant of a refrigerator--that is, not for use according to the invention in a vehicle air-conditioning system--is composed, depending on the performance requirement, of one component group or several identical component groups which are then arranged according to the features of the preamble of claim 1 and are interconnected in cross-countercurrent. Each one of the component groups includes only one row of tubes and they are physically separated from one another and thus also with respect to thermal conduction.
If adjacent component groups are completely mechanically decoupled from one another and thus automatically also with respect to thermal conduction, problems arise with respect to the mechanical strength of the entire liquefier and also considerably higher manufacturing costs since practically at least two separate liquefiers must be produced and connected with respect to flow in the smallest possible, unchanged space. These problems become considerably more serious in connection with liquefiers for the coolant of a vehicle air-conditioning system due to their small dimensions in adaptation to the small space available in motor vehicles.